1. Field of the Invention
This invention relates to an intracranial pressure transducer of a small size, which can accurately detect an internal pressure and a pulse pressure in a skull, without damaging a dura under a skull of a body to be measured.
2. Description of the Prior Art
The head of a human being or a body to be measured is of supreme importance for the life and social life thereof. The brain or cerebrum is retained in a container consisting of a skull and a spinal cord. This container is filled with a liquid which is referred to as a cerebrospinal fluid (C.S.F.), and the cerebrum floats in the liquid. An organism membrane referred to as a dura or duramater is present inside the skull for maintaining air tightness of a ventricle within the skull.
It is known in the field of cerebro-surgery and cerebro and neuro-surgery that an internal pressure within a skull is increased (intracranial pressure exacerbation) due to external causes such as a blow to the head of a human being, traffic accidents and the like, or internal causes such as epidural hemorrhage, encephaloma and the like. Such an increase in internal pressure in a skull is mainly attributable to an abnormal condition in the circulatory system of the cerebrospinal-fluid. When an increase in internal pressure in the skull affects a human body lightly, there occurs headache, dizziness, vomiting or the like. Further, when an increase in internal pressure in the skull severely affects a human body heavily, there results severe headache, consciousness loss, retardation of growth of the brain occuring from compression of the brain, anaerosis and the like.
In these fields, an internal pressure in a skull has been measured according to various methods for studying causes of a disease as well as for the maintenance of the life of a human body.
One of the methods for deriving an internal pressure information from the interior of a skull of a human body is to pierce an injection needle into a lumbar region of a body to be measured (lumbar puncture), and then a water level is measured by a water column manometer which is connected to the injection needle, for measuring an internal pressure in the skull.
This method is simple but suffers from inaccurate response to an internal pressure in a skull, because its measurement is carried out at the lumbar region apart a considerable distance from a head. Particularly in the case of internal pressure in a skull which is abnormally high, lumbar puncture results in a sharp reduction in intracranial pressure, and hence the brain is pushed down, with the result that the brain presses a circulatory system for a cerebrospinal fluid, thereby jeopardizing the life of a human body. This method is dangerous in most cases.
Recently, it has been a general practice for the measurement of an internal pressure in a skull to drill a hole in a skull cap and then to insert a tube into a ventricle by breaking a dura (dura-mater) under a skull for measuring a water level in a water column manometer connected to the tube. This method is advantageous only in view of the fact that an internal pressure in the skull is directly measured in a head. However, the dura should be broken to allow insertion of the tube and thus the brain is damaged, with an accompanying danger of cerebromeningitis due to microbism, as well as lack of safety.
When an internal pressure in a skull is further accurately measured, a high level of skill is required for a doctor, and considerable stress is imposed on a patient depending on a health condition (dying, weakness). Accordingly, the measurement for a long period of time appears impossible.
Recently, there has been proposed an electric-pressure transducer for accurately measuring an internal pressure in a skull in place of a water column manometer. In either case, the measuring method itself remains unchanged, so that the aforesaid shortcoming can not be avoided. As a result, an electrical pressure transducer for measuring an internal pressure in a skull has not yet reached a practical stage of clinical use, and fails to find a satisfactory use. There has arisen, accordingly, a demand for an electrical pressure transducer which overcomes the aforesaid shortcomings.
The measurement of an internal pressure and a pulse pressure in a skull of a human body according to the present invention is based on a discovery that an internal pressure as well as a pulse pressure within a skull can be measured without damaging an important dura according to the steps of: forcing a resilient, flat pressure-receiving layer, which houses a semiconductor pressure-electric transducing element, against a dura encompassing a brain under the skull; maintaining a balance between a force to press the dura or a pressure of a pressure receiving layer and a tension of the dura; and converting a pressure in a balanced condition which corresponds to an internal pressure and a pulse pressure in the skull into an electrical signal by the semiconductor pressure-electric transducing element. This intracranial pressure transducer provides a high degree of safety and is well adapted for use for periods of time, with an accompanying high accuracy in measurement.
The intracranial pressure transducer of the present invention comprises a casing including an annular member having a screwed part on an outer wall thereof for fitting and securing to a skull of a body, a pressure-electric transducing portion comprising a supporting member which is inserted within an inner wall of the casing and is tightly fixed to a predetermined upper portion from a tip portion of said casing, and which has a hole of predetermined diameter, a thin strain sensing member bonded to a lower surface of the supporting member having the hole in order to close the hole, at least one strain sensitive element for converting the strain of the strain sensing member to an electrical signal provided at a strain sensing region, which region corresponds to the hole of the supporting member, on the thin strain sensing member, lead wires connected to the strain sensitive element and a receiving connector provided at a top portion of the casing, and a pressure receiving layer comprising resilient material and filling a concave portion formed by an inner wall of the tip portion of the casing, the lower surface of the supporting member, and the lower surface of the thin strain sensing member, and an indicating circuit for indicating the intracranial pressure in response to an output of the strain sensitive elements, comprising an amplifier circuit connected to said lead wires within said pressure-electric transducing portion through connector means, and indicating means.
The intracranial pressure transducer having the above simple structure according to the present invention converts the intracranial pressure of a cerebrospinal fluid to the internal pressure of the pressure receiving layer by Coplanar method which maintains the dura to be coplanar by the depression of the pressure receiving layer of the transducer against the dura, applies the internal pressure of the pressure receiving layer to the strain sensing member, supplies the electrical signal by the strain sensitive element in response to the internal pressure of the pressure receiving layer, and accurately and safely indicates the intracranial pressure on the indicating means.
The present invention further provides for easier treatment and maintenance than prior intracranial pressure transducers utilizing a pressure chamber filled with fluid such as oil, which chamber is in contact to the strain sensing member. Generally, the pressure chamber of intracranial pressure transducer is formed with a rubber diaphragm and the rubber diaphragm is corroded by the oil. So, this transducer has a possibility of leakage of the oil from the hole and crack of the diaphragm within the body, and is defective with respect to human protection. Further, with this transducer, it is necessary to control the oil and it is troublesome to treat and maintain the same such that the life of the transducer is short.
On the other hand, in an intracranial pressure transducer having a metal diaphragm, accurate and stable measurement is impossible by directly detecting abnormal and concentrated pressure (stress) due to the projections and wave surface such as blood vessels of the dura.
The present invention easily solves these above-noted problems.